Systems which involve liquid flow are frequently are plagued with blockages and restrictions caused by foreign contaminants. Because liquid systems cannot remain contaminant free, a liquid filtering system is always required. Contaminants within a fluid/liquid system exist due to many factors. The simple process of assembling and handling the fluid system parts and components often introduces undesirable contaminants. The act of turning a threaded pipe or fitting into a mating component often shears off thread burrs, allowing the burrs to flow through the liquid system. Small pieces of weld slag, grains from the foundry or cast core sand may be involved. Foreign matter may be deposited during storage of replacement piping and then released during assembly. Component wear and tear will introduce contaminants into the system. Contaminants may be introduced along with the desired fluids when fluid is added to the system. For these and many more reasons, a liquid system requires that a filtering system be in place and maintained.
The ideal liquid filtering system will remove all foreign contaminants from the liquid without impeding fluid flow through the system as demanded by the pump. Other desirable characteristics include: low cost, high capacity, small size and easy maintainability. There are three main types of filtration systems: mechanical, adsorbent, and absorbent. Typical liquid processing systems include some combination of these three types of filter.
Mechanical filters are probably the most common in industrial liquid systems. The liquid is forced by pressure through the filter element. The filter is composed of micro-openings, pores or tortuous passages that block and capture larger sizes particles. This type of filter, commonly referred to as a surface type filter, is normally composed of woven fabric, metallic or synthetic screens and/or absorbent paper or paper like materials. The constituent parts of such filters must be compatible with the process liquid and with the expected contaminants. Fire resistance (as applicable), resistance to collapse (due to pressure differential), and compatibility with system temperature are other important issues to consider in choosing a filter. Filters may be constructed of pleated stainless steel, Monel wire and synthetic woven materials.
Adsorbent filters are typically include porous materials such as cotton, paper, wood, cloth, asbestos, etc. Adsorption is a process wherein contaminants adhere to the surface or surfaces of a filter member rather that being trapped within a filter member. In general this type filter is used to filter fine soluble's and may be designed to allow selected dirty liquid through relatively thick layers with an increase in compactness of the filter material in the direction of flow.
Absorbent filters function by absorbing and trapping contaminants within a filter member. Examples of absorbent filter material include fuller's earth, boneback, ceramic, graphite, grapheme, charcoal, activated carbon, activated clay, copper, silver, platinum, gold, or other metals or metal compounds, chelating agents, or chemically treated organic mediums applicable to the filtration of oil, fuel, syngas, natural gas or other petroleum or alcohol based products. This type of liquid filtering system may be in the form of gravity feed bed or even a cartridge type installation. This system presents a large surface area through which the liquid flows. The insoluble oxidation products and solid contaminants are removed by size filtration and absorption.